The invention relates to an actuating mechanism for a parking brake, comprising a handbrake lever that is positioned pivoting on a bearing block, a brake setting device provided with a locking segment secured to the bearing block and a movably positioned locking pawl, and an actuating linkage positioned inside the handbrake lever which can be activated by a push button to move counter to the force of a spring.
An actuating mechanism of this type is known from German patent document DE 195 21 159 C2. This actuating mechanism comprises a handbrake lever that is positioned pivoting on a bearing block. A single actuating rod, which engages in a brake-setting device, is used as an actuating linkage for operating the parking brake. The actuating rod extends inside a tubular holder for the handbrake lever. The front end of the actuating rod is provided with a push button, which projects past the tubular holder and can be pushed by a person operating the brake.
The brake-setting device consists of a locking segment and a locking pawl. The locking segment is attached to the bearing block and is provided with a line of ratchet teeth. The locking pawl is positioned pivoting on a bearing journal for the handbrake lever and is pre-stressed by means of a spring element, wherein the locking pawl is positioned on the bearing journal so that it is divided into two pivoting arms, which extend on both sides of the bearing journal. One end of the first pivoting arm is provided with detents, which engage in the ratchet teeth on the locking segment to secure the locking pawl on the locking segment. The end of the second pivoting arm is attached via a link joint to the lower end of the actuating rod.
The handbrake lever is pivoted in order to operate the parking brake. The pivoting movement is transmitted via the actuating rod to the locking pawl. In an end position, the locking pawl engages in the locking segment and secures the handbrake lever in the respective position.
To release the handbrake lever from this position, the push button is pushed to release the locking pawl from the locking segment, thereby allowing the handbrake lever to be moved back to its starting position.
Actuating mechanisms of this type have the disadvantage that during the pivoting movement of the handbrake lever, the actuating rod, and thus also the push button, is moved in an axial direction and that this movement of the push button is visible to the operator. A movement of this type is undesirable, particularly if actuating mechanisms of this type are installed in passenger vehicles in the upper price range. The push button movement results from the locking pawl with its detents moving along the locking segment with the line of ratchet teeth during the pivoting of the handbrake lever, thereby generating an oscillating movement of the locking pawl, which is transmitted to the actuating rod.
A different actuating mechanism of the generic type is known from German patent document DE 20 2004 014 356 U1. The brake-setting device for this actuating mechanism is designed such that the push button on the actuating linkage is decoupled from the locking pawl movement along the locking segment during the pivoting of the handbrake lever and thus remains in the idle position. The locking pawl provided for this embodiment is positioned with its upper end pivoting on the handbrake lever. The lower end of the locking pawl is provided with a detent, which can be made to engage in the ratchet teeth on the locking segment.
An elongated hole is worked into the lower region of the locking pawl to provide a connection to the actuating linkage. A bearing pin that is attached to the front end of the actuating linkage projects into this elongated hole. The length of the elongated hole considerably exceeds the diameter of the bearing pin, so that in the actuation direction of the linkage, the bearing pin is guided with play inside the elongated hole.
In one engaged position of the handbrake lever, the detent on the locking pawl is pushed against the ratchet teeth of the locking segment with the aid of a catch spring that acts upon the locking pawl. In addition, the force of a spring, against which the push button can be activated, will push the bearing pin on the actuating linkage against the front edge, facing the locking segment, of the elongated hole in the locking pawl and help push the locking pawl against the locking segment.
For the push button activation counter to the spring force, the bearing pin, which is moved against the rear edge of the elongated hole releases the locking pawl from the engaged position in the locking segment. If the handbrake lever is subsequently pivoted, the bearing pin can freely oscillate against the actuating linkage in the elongated hole in the locking pawl. As a result, the oscillating movement generated during the pivoting of the handbrake lever is not transmitted to the actuating linkage and the push button remains in the idle position.
To achieve a secure decoupling of the push button from the oscillating movement of the locking pawl during the pivoting movement, it is necessary for the bearing pin to move without friction inside the elongated hole in the locking pawl. For this, the contour of the elongated hole is adapted to the movement curve of the bearing pin. The disadvantage of this type of arrangement, however, is that it is extremely sensitive to malfunctions. As a result of tolerances in the structural components, which always exist and in particular include tolerances in the actuating linkage components, the movement curve for the front end of the actuating linkage and thus also for the bearing pin changes and a non-frictional guidance of the bearing pin in the elongated hole is no longer ensured. In the final analysis, this leads to problems with the operation of the brake setting device. In particular, it means that a secure decoupling of the push button from the oscillating movement of the locking pawl is no longer ensured. The problem could, in principle, be solved by providing a great deal of play for the guidance of the bearing pin inside the elongated hole, even in transverse direction to the actuation direction for the actuating linkage. However, changing the elongated hole in this way would result in a lack of forced guidance between locking pawl and actuating linkage, thus reducing the function of the actuating mechanism.